A Geometric Morphometric Study on Sexual Dimorphism in Viscerocranium

Abstract

The level of sexual dimorphism manifested by human bones is an important factor for development of effective sex estimation methods. The aim of the study was to investigate the sexual dimorphism in the size and shape of the viscerocranium using geometric morphometric techniques. It also aimed to explore the sex differences in distinct viscerocranial regions and to establish the most dimorphic region with regard to size and shape. Computed tomography images of 156 males and 184 females were used in the study. Three-dimensional coordinates of 31 landmarks were acquired. Five landmark configurations were constructed from the viscerocranium and its orbital, nasal, maxillary, and zygomatic region. Generalized Procrustes superimposition, principal component analysis, and discriminant analysis were applied to each configuration. The significance of the sex differences in size and shape was assessed and significant differences were found in all configurations. The highest accuracy was obtained from both shape and size of the whole viscerocranium. Based on size only, the highest accuracy was achieved by the nasal region. The accuracy based on shape was generally low for all configurations, but the highest result was attained by the orbital region. Hence, size is a better sex discriminator than shape.

Keywords: 3D landmarks; computed tomography; geometric morphometrics; sexual dimorphism; viscerocranium.

Figure 1

Landmarks of the viscerocranium: (a) frontal view; (b) lateral view.

Figure 2

PCA scatterplot: landmark digitization error (three trials of 40 specimens).

Figure 3

PCA scatterplot for the viscerocranium configuration. The wireframes illustrate the shape variation along the axis of PC1. Male crania—blue triangles; female crania—red rhombs; extreme shape configurations—purple wireframes; mean shape configuration—light blue wireframe.

Figure 4

PCA scatterplot for the configuration of the orbital region. The wireframes illustrate the shape variation along the axis of PC1. Male crania—blue triangles; female crania—red rhombs; extreme shape configurations—purple wireframes; mean shape configuration—light blue wireframe.

Figure 5

PCA scatterplot for the configuration of the nasal region. The wireframes illustrate the shape variation along the axis of PC1. Male crania—blue triangles; female crania—red rhombs; extreme shape configurations—purple wireframes; mean shape configuration—light blue wireframe.

Figure 6

PCA scatterplot for the configuration of the maxillary region. The wireframes illustrate the shape variation along the axis of PC1. Male crania—blue triangles; female crania—red rhombs; extreme shape configurations—purple wireframes; mean shape configuration—light blue wireframe.

Figure 7

PCA scatterplot for the configuration of the zygomatic region. The wireframes illustrate the shape variation along the axis of PC1. Male crania—blue triangles; female crania—red rhombs; extreme shape configurations—purple wireframes; mean shape configuration—light blue wireframe.